This invention relates generally to multivibrators, and, more particularly, to a voltage-controlled sweep multivibrator which incorporates within the circuit a "digital" gate.
A multivibrator is a form of relaxation oscillator consisting normally of two or more active devices, such as transistors or vacuum tubes, interconnected by electric networks. In a multivibrator a portion of the output voltage or current of each active device is applied to the input of the other with such magnitude and polarity as to maintain the devices alternately conducting over controllable periods of time. Such an electronic circuit has an extremely broad range of applications, in such equipment as oscilloscopes, telemetry systems, computer terminals, television cameras and signal processors, electronic music systems, etc.
In the past, the conventional unijunction transistor (UJT) multivibrator utilized a resistor as a means of controlling the capacitor charging current. This method, however, limits the range of sweep repetition rates (SRR) that can be obtained since:
A. If the resistance value is too large, the charging current will be too small to overcome inevitable leakage losses in the capacitor and UJT, so the capacitor will never charge to the UJT switching voltage; and
B. If the resistance value is too small, the charging current will exceed the UJT latching current, so the UJT will never switch OFF.
UJT multivibrators using transistors as charging current sources have the major advantage over the simple types referred to hereinabove in that their sweep output waveform is a linear sawtooth rather than an exponential sawtooth. However they do not escape the limitations on SRR imposed by the leakage and latching current considerations as set forth above.
Therefore, in order to achieve high performance many components had to be used, thus, creating a great expense. Although UJT multivibrators offer obvious benefits in sweep circuitry, their performance cannot match conventional sweep generators, particularly at high speeds.